This invention relates to a new process for preparing a polycyanoaryl ether powder. More particularly, it is concerned with a process for preparing a finely divided polymer powder sufficiently purified without any steps for grinding the resultant polymer.
A polycyanoaryl ether is an engineering plastic with superior heat resistance and has been widely used as a material for electric and electronic equipments or mechanical components.
There is disclosed in Japanese Unexamined Patent Publication No. 14270/1972 a process for preparing the polycyanoaryl ether by reacting dinitrobenzonitrile with 2,2-bis(4-hydroxyphenyl)propane. However, the polymer thus produced has a problem in that sufficient heat resistance could not always be provided. Further, in the above process, when hydroquinone or dihydroxydiphenyl is employed as a dihydric phenol, there could not be produced a polymer having a sufficiently high molecular weight.
In view of the above state of prior art, the inventors had already proposed a process for preparing a polycyanoaryl ether with a high molecular weight from a dihalogenobenzonitrile and dihydric phenols (see Japanese Unexamined Patent Publication Nos. 144328/1985 and 147439/1985, Japanese Patent Application No. 165655/1984). However, there was needed a mechanical grinding of the resulting polymer at the purification stage of the polymer and there remained much room for improvements. The prior processes consumed large amounts of energy during the grinding step and the relatively coarse particle size of the resultant powder lead to insufficient purification.